JPS5811307B2 - Short circuit arc welding equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for short-circuit arc welding by using at least one welding current power source and feeding welding wire from a reel through a welding wire guide to a workpiece to be welded. be.

US Pat. No. 2,886,696 proposes an arc welding method in which welding material in the form of a welding wire is continuously fed to a workpiece.

A welding power source is connected between the work piece and the welding wire, thereby supplying electric power to melt the Caloe piece and the welding wire.

When the voltage and current of the welding circuit and the feeding speed of the welding wire are appropriately selected, the tip of the welding wire melts to form a bead, that is, a droplet, which is transferred to the workpiece and formed on the surface of the workpiece. Absorbed into the weld pool.

This results in a regular cycle of arc ignition, bead formation, shorting between the bead and the weld pool, and generation of a short-circuiting current, which fuses the bead from the solid part of the welding wire, after which the next arc point An arc occurs.

The cycle time; arc time and short circuit time can vary depending on various parameters.

The reason for this is that the welding process itself automatically adapts to the changed conditions within predetermined limits.

A related disadvantage is that the size of the bead always changes after such adaptation.

In extreme cases where the arc power is high, the weld pool becomes relatively large and the bead becomes quite large at a relatively long distance from the weld pool, and during the next short circuit this bead breaks up into droplets and falls on the workpiece surface. Splash on top.

To eliminate this splatter effect, it is proposed in US Pat. No. 3,275,797 to provide a splatter mitigation control circuit in the welding circuit, thereby limiting the short circuit current to a value less than the arc current.

The present invention first forms a bead of approximately constant size during each arc-shorting cycle, and this bead is removed before the shorting current (which has the known effect of interrupting fusion with the welding wire) is generated. This was done based on the recognition that it is necessary to have sufficient absorption into the molten pool.

Therefore, in the apparatus of the present invention, the arc is maintained between the welding wire and the work piece during the time interval Tb, and approximately constant power is supplied during this period, thereby forming a weld bead of approximately constant size on the welding wire. and then feeding the welding bead into the molten pool of the workpiece at a welding wire feeding speed during the time interval Tw,
It is characterized in that the short-circuit current that fuses the bead and the welding wire is supplied after a certain delay time Td following the instant of the short-circuit.

According to this device, the same amount of material always falls from the welding wire in each cycle, and there is almost no scattering effect.
There is also the advantage that the automatic adjustment characteristics of the welding process are maintained as they are when parameters change.

In the device of the present invention, the arc is further supplied by the first power source which has a no-load voltage higher than the arc voltage during a certain period of time Tb and current source characteristics, that is, high internal impedance, and the short circuit current is supplied with a voltage lower than the arc voltage and a low internal impedance. Mainly supplied by a second power source having a second power supply.

The advantage of this configuration is that a constant arc power is easily obtained with a welding power source that has the characteristics of a current source due to its relatively high impedance and has a descending characteristic, so that the arc voltage remains approximately constant during the process. Coupled with this assumption, a constant arc power Eb/Ib can be obtained. Therefore, simply by keeping the time interval Tb constant, the arc is kept constant and the arc power per bead becomes arc voltage Bb and arc current Ib.
and time Tb.

In the device of the present invention, the occurrence of arc voltage between the welding wire and the work piece can be detected and used advantageously to determine the time Tb, and the occurrence of low voltage, ie short circuit voltage, can be detected between the bead and the molten pool. It can be used to determine the short-circuit instant during

In the device according to the invention it is advantageous to use controllable semiconductor switches in the welding current circuit and to control these by a control unit regulating the times Tb and Td.

In this case it is preferred to use a silicon controlled rectifier.

In a preferred embodiment of the device of the present invention, the first power source is a current source, and the second power source is a current source.
A power source is used as a voltage source, and the positive terminal of the first power source is directly connected to the welding wire through two anti-parallel connected silicon-controlled rectifiers using the positive terminal of the second power source as a welding current switch,
The negative terminal of each power supply is connected to the workpiece, and the control unit first turns on one silicon-controlled rectifier for each arc-short cycle to extinguish the arc and causes the second power supply to dissipate the current from the first power supply. , time interval T
After w+Td, the other silicon controlled rectifier is turned on to provide the short circuit current.

In another embodiment of the device of the invention, the positive terminal of the first power supply is connected to the welding wire through a first silicon-controlled rectifier, and the positive terminal of the second power supply is connected to the first silicon-controlled rectifier and the anti-parallel circuit of diodes. connected to the positive terminal of the power supply, the control unit turns on the second silicon-controlled rectifier after a time interval Tb in each arc-short circuit cycle, and after a time interval Tw+T.
Turn on the first silicon controlled rectifier after d.

Both devices have the advantage of automatically turning off the silicon-controlled rectifier at the correct moment using the low voltage of the second power supply without the use of complex commutation circuits.

This makes the control unit extremely simple and can consist, for example, of two Schmitt triggers and two monostable circuits; in another preferred embodiment of the device according to the invention, the control unit has one input terminal. connected to the welding wire and the workpiece, the control unit further comprising a first Schmitt trigger circuit having a trigger level lower than the arc voltage connected to the input terminal, and a controllable semiconductor switch connected to the first Schmitt trigger circuit. a first monostable multi-bi break circuit connected to the control input terminal and determining the time interval Tb; a second Schmitt trigger circuit connected to said input terminal and having a trigger level lower than the arc voltage but higher than the short circuit voltage; 2 Schmitt trigger circuit and the time interval Td connected to the control input terminal of the controllable semiconductor switch
and a second monostable multivibrator circuit for determining.

When the time intervals Tb and Td are determined by detecting the arc occurrence instant and the short circuit instant from the voltage between the welding wire and the work piece, the welding wire feeding time Tw and the welding wire feeding time Tw and Even if the instant of bead fusing due to short circuit current changes, the operating cycle of the device adapts to these changes to form a bead of uniform size and to melt the bead after a portion of the bead has been supplied to the fusing pool. If done correctly, you will get a uniform and high quality weld.

The invention will be explained with reference to the drawings.

FIG. 1 shows a reference example to facilitate understanding of the present invention.

A welding current is supplied from a power source 1 to a welding wire guide 5 that guides a welding wire 6 through terminals 2 and 3 and a switching unit 4 to form a welded joint on a workpiece 7.

The welding current varies according to a regular cycle consisting of arc current intervals and short circuit current intervals.

The heat generated by these currents causes a weld pool 8 to form in the workpiece 7 and causes the welding wire 6 to melt in the area 9.

The welding wire 6 is supplied from a reel 10 driven by a motor control unit 11 via a welding wire guide 5.

The control unit 12 supplies a control signal to the switching unit 4 via the connection line 13 to apply the welding current to the connection line 14.
and 15 in response to measurement signals received by the welding circuit.

The operation of this device is as follows.

Control unit 12 switches on switching unit 4 to apply a sufficiently high voltage between welding wire 6 and workpiece 2 to maintain an arc in area 9 .

The arc voltage Eb and the arc current Ib are measured by the control unit 12, and the types of these three parameters, which can change the arc connection time Tb as necessary, are determined so as to be constant.

Therefore, the supplied power remains constant.

With the correct settings, the weld pool 8 is heated with this power and the tip of the welding wire melts to form a bead, i.e. a droplet, which is connected to the arc-short-arc sequence associated with such a welding process. The arc, which always forms with the same magnitude during the arcing period, is then extinguished by the switching unit 4, which interrupts the welding circuit.

The bead is transferred to the weld pool so that welding wire 6 is fed at a predetermined speed.

The bead comes into contact with the molten pool after a waiting time Tw, this short-circuit instant is measured in the control unit 12, and after a delay time Td the switching unit 4 is switched on by the control unit 12 and a short-circuit current flows from the power supply 1 in the welding circuit. Initially, this causes the bead in area 9 to heat up further, causing the bead to fall off the welding wire and an arc again being obtained between the welding wire and the weld pool.

Thereafter, the above-described process is repeated.

It is therefore clear that control of the short arc cycle as described above, in which a bead of constant size is always fed into the weld pool and then interrupted, provides a more uniform and better quality weld under varying conditions.

In particular, the occurrence of scattering is almost suppressed. FIG. 2 shows a second reference example to facilitate understanding of the present invention, and portions of the block diagram in FIG. 1 are designated by the same reference numerals.

The power supply 1 is divided into a power supply 1a with a high internal impedance and a voltage higher than the arc voltage of zone 9, and a power supply 1b with a voltage lower than the arc voltage and a low internal impedance.

In FIG. 2, the switching unit 4 shown in FIG. 1, which has a program function and turns on and off the correct voltage and current, is simplified to a switch 4a and a switch 4b.

Although these switches are shown as mechanical switches, they are preferably controllable semiconductor switches.

According to the invention, it is advantageous to use the power source 1a since the arc power during the cycle must be constant.

The reason is that in this case the product of Eb and Ib is constant in advance.

In this case, it is sufficient to close the switch 4a during the fixed time interval Tb.

This greatly simplifies the control of the control unit 12 of FIG.

By closing the switch 4b, a short circuit current is supplied from the power source 1b.

The voltage of this power source only needs to exceed the short-circuit voltage between the welding wire 6 and the workpiece, and therefore can be significantly lower than the arc voltage.

FIG. 3 shows an embodiment of the device according to the invention, using silicon controlled rectifiers 4a and 4b as switches.

The power source 1a can be a simple welding power source having a rectifier circuit and a self-inductance that obtains the falling characteristic of the current source circuit.

This type of welding power source provides a substantially constant arc current, but has the troublesome characteristic of being slow and unable to be turned on and off quickly due to self-inductance.

Furthermore, it is known that silicon-controlled rectifiers cannot be turned off in the case of inductive loads without special measures.

Despite these drawbacks, the circuit of FIG. 3 is distinguished by its simplicity.

A power source 1a is directly and permanently connected to the welding wire 6 and the workpiece 7.

An arc current switch 4a is connected within the lead wire from the welding wire guide 5 to the power source 1b.

As soon as an arc occurs in the area 9 and an arc voltage appears, this voltage is measured in the control unit 12 via the conductor 14 and a timing circuit is started which determines, for example, the time interval Tb.

After this time interval, the silicon controlled rectifier 4a is triggered,
Connect the power source 1b to the welding wire guide 5.

The voltage of the power supply 1b is lower than the arc voltage, and the voltage of the power supply 1b is lower than the arc voltage.
&! The arc is extinguished because it has a high internal resistance.

At this time, the current from the current source 1a flows through the thyristor 4a to the power supply 1b and is consumed there.

The power supply 1b can be configured with a main transformer with a rectifier,
Since this cannot draw current, it is necessary to provide a resistor R2 and a buffer capacitor C if necessary.

During this time, a short circuit occurring between the welding wire and the molten pool 8 is detected by the control unit 12 via the conductor 14 and a timing circuit is activated in the control unit which determines the time interval Td.

After this time interval, the silicon-controlled rectifier 4b connected anti-parallel to the silicon-controlled rectifier 4a is triggered.

During the delay time Td, the current from the vehicle source 1a flows through the short circuit in zone 9 due to said short circuit.

This short-circuit voltage is lower than the supply voltage of power supply 1b, so that silicon-controlled rectifier 4a can be turned off.

However, since the silicon-controlled rectifier 4b is driven into conduction, a short-circuit current will then flow from the power supply 1b through the zone 9, promoting the extinguishing of the silicon-controlled rectifier 4a.

Furthermore, the welding bead falls off the welding wire 6, thereby interrupting the short circuit between the welding wire and the workpiece.

The voltage between them then increases until an arc occurs, and since this voltage is higher than the voltage of power supply 1b, silicon-controlled rectifier 4b is turned off.

The above cycle is then repeated. It is necessary to provide a resistor R1 in series with the silicon controlled rectifier 4b to limit the short circuit current.

FIG. 4 shows a modification of the device of FIG. 3, in which a diode D is used instead of the silicon-controlled rectifier 4b, and the silicon-controlled rectifier 4c remains connected to the welding wire guide 5 and 1 to the silicon-controlled rectifier 4a and the diode D. and the positive voltage conductor of the power supply 1a.

Therefore, with this device, it is possible to prevent any current from flowing from the power supply to the short circuit area during the delay time Td.

In this case, the silicon-controlled rectifier 4c is cut off, and the silicon-controlled rectifier 4a remains conductive to supply current from the power source 1a to the power source 1b.

The occurrence of a short circuit is measured on the lead 14 and a second Schmitt trigger circuit S2 in the control unit 12 is triggered due to the low short circuit voltage.

As a result, the monostable circuit M2 starts, and after a time interval Td (returns to this stable state, the trigger transmits the pulse to the trigger unit T2c).
This provides a trigger pulse to the silicon controlled rectifier 4C via the isolation transformer.

The voltage on conductor 17 is equal to the voltage on power supply 1b, so silicon controlled rectifier 4cc-s turns on and reduces the voltage on conductor 17 by the short circuit voltage O.

As a result, the current in power supply 1a flows through silicon-controlled rectifier 4c, diode D is turned on again, and silicon-controlled rectifier 4a is not turned on.

At this time, a short-circuit current is obtained from the power source 1b, and this current breaks the connection between the welding wire 6 and the workpiece 7 after the short-circuit time Tks, so that the voltage on the conducting wire 17 increases again to the arc voltage.

The silicon controlled rectifier 4c therefore remains conductive.

The generation of the arc voltage is measured via the conductor 14, and this voltage is connected to the first Schmitt trigger circuit S1 in the control unit 12.
, this Schmitt trigger S1 triggers the monostable circuit M1 to supply a control signal to the trigger unit T1 after a time interval Tb, after which the silicon-controlled rectifier 4
a is turned on via the transformer of unit T1.

The voltage on conductor 17 drops below the arc voltage and power supply 1b
, the arc in area 9 is extinguished and silicon-controlled rectifier 4c is no longer conducting and is turned off.

This is followed by adjustment of the standby time Tw, short circuit, and delay time Td, after which the above cycle is repeated.

For the purpose of explaining the above, FIG. 5 shows the voltage and current of a known uncontrolled short arc welding device.

Waveform diagram a shows the voltage between the welding wire and the workpiece as a function of time.

This voltage alternately takes the value Eb of the arc voltage during time Tb and the value Ek of the short-circuit voltage during time Tk.

This voltage waveform is stylized into a square wave.

The waveform diagram in Figure 5 shows the arc current I corresponding to the voltage waveform a.
b and short circuit current Ik are shown.

The cycle time is Tc = Tb + Tk, where both Tb and Tk can vary depending on various influences affecting the welding process.

FIG. 6 is a waveform diagram corresponding to FIG. 5 when the device of the present invention is used.

For example, the arc time Tb is maintained constant.

This is followed by a waiting time Tw (which time can vary) and then by a short-circuit instant Tk, which instant is detected and a certain delay time Td occurs, after which the short-circuit current Ik is increased over a time interval Tks (this time (time intervals may vary).

Therefore, the cycle time Tc may vary depending on Tw and Tks due to external changes, changes in welding wire supply speed or power supply voltage, for example.
may change accordingly.

Therefore, operator control, uniform bead formation even when welding parameters such as changes in power supply voltage or changes in welding wire feed rate change, and bead fusing shorts that are fed after the bead has partially entered the weld pool. Proper delay supply of current results in uniform and high quality welding.

[Brief explanation of the drawing]

1 and 2 are block diagrams of reference examples to facilitate understanding of the present invention, FIG. 3 is a block diagram of an embodiment of the apparatus according to the present invention, and FIG. 4 is a block diagram of an embodiment of the apparatus according to the present invention. A block diagram of the embodiment, FIG. 5 is a welding voltage and current waveform diagram of a known device, and FIG. 6 is a welding voltage and current waveform diagram of the device of the present invention. 1.1a, 1b...Power supply, 4...Switching unit, 5...Welding wire guide,
6... Welding wire, 7... Processed piece, 8
...... Molten pool, 10... Reel, 11.
...Motor control unit, 12...Control unit, 4a, 4b, 4c...Silicon controlled rectifier, D...Diode, S1, S2...
...Schmitt trigger circuit, M1, M2...
Monostable circuit, T1. T2...Trigger unit,
Eb... Arc voltage, Ib... Arc current, Ek... Short circuit voltage, Ik... Short circuit current, Tb... Arc time interval , Tw...
...Waiting time interval, Td... Delay time, Tks...
...Short circuit current time interval.

Claims (1)

[Scope of Claims] 1. A power supply device that supplies welding power between a welding wire and a workpiece, a device that feeds the welding wire to the workpiece, and a supply of power from the power source to the welding wire and the workpiece. In a short-circuit arc welding device comprising a switching unit that controls a switching unit and a control unit that controls the switching unit, the power supply device includes a first power supply having a no-load voltage higher than an arc voltage and a relatively high internal impedance. , a second power source having a voltage lower than the arc voltage and a relatively low internal impedance is provided, the positive terminal of the first power source is directly connected to the welding wire, and the switching unit has a positive terminal of the first power source and a second power source having a relatively low internal impedance. a first switch connected between the positive terminal of the second power source and a second switch connected between the positive terminal of the second power source and the welding wire; a first timing circuit that detects an arc voltage occurring between the workpieces and generates a first control signal to close the first switch after a predetermined time Tb from the moment when the arc voltage is generated;
Short-circuit arc welding, characterized in that a second timing circuit is provided that detects a short-circuit voltage generated between a welding wire and a workpiece and generates a second control signal to close the second switch after a predetermined time Td from the instant of the short-circuit. Device. 2. A power supply device that supplies welding power between the welding wire and the workpiece, a device that feeds the welding wire to the workpiece, and a switching unit that controls the supply of power from the power source to the welding wire and the workpiece. , a short circuit arc welding apparatus comprising a control unit controlling the switching unit, wherein the power supply includes a first power supply having a no-load voltage higher than the arc voltage and a relatively high internal impedance, and a voltage lower than the arc voltage. and a second power supply having a relatively low internal impedance; the switching unit includes a first switch connected between a positive terminal of the first power supply and a positive terminal of the second power supply; a diode connected in parallel with the switch in the opposite direction; and a second switch connected between the positive terminal of the first power source and the welding wire; a first timing circuit that detects the arc voltage generated at the arc voltage and generates a first control signal to close the first switch after a predetermined time Tb from the moment when the arc voltage is generated; and a first timing circuit that detects the short circuit voltage that occurs between the welding wire and the workpiece. A short-circuit arc welding apparatus characterized in that a second timing circuit is provided for generating a second control signal for closing the second switch after a predetermined time Td from the instant of the short-circuit. 3. The apparatus of claim 1, wherein the control unit has its input terminals connected to the welding wire and the workpiece, and wherein the control unit has a trigger level lower than the arc voltage connected to the input terminals. a first Schmitt trigger circuit; a first monostable multivibrator circuit for determining the time interval Tb connected to an output terminal of the Schmitt trigger circuit and a control input terminal of a controllable semiconductor switch constituting the first switch; a second Schmitt trigger circuit having a trigger level significantly lower than the arc voltage but higher than the short circuit voltage connected to the input terminal;
A short-circuit arc welding device comprising: a second monostable multivibrator circuit for determining the time interval Td, which is connected to a control input terminal of a controllable semiconductor switch constituting the switch. 4. The apparatus of claim 2, wherein the control unit has its input terminals connected to the welding wire and the workpiece, and wherein the control unit has a trigger level lower than the arc voltage connected to the input terminals. a first monostable multivibrator circuit for determining the time interval Tb connected to an output terminal of the Schmitt trigger circuit and a control input terminal of a controllable semiconductor switch constituting the first switch; , a second Schmitt trigger circuit having a trigger level significantly lower than the arc voltage but higher than the short circuit voltage connected to the input terminal; and a controllable semiconductor switch constituting the output terminal of the second Schmitt trigger circuit and the second switch. a second monostable multivibrator circuit for determining the time interval Td connected to a control input terminal of the short-circuit arc welding apparatus.